The present invention relates to an alkaline zinc electroplating bath and process and to novel organic compounds useful as additives therein. The novel compound of this invention is an alkylated hydroxyl aryl compound which can be advantageously employed for a brightening and/or stain preventing effect in cyanide-containing or cyanide-free alkaline zinc electroplating baths.
Alkaline zinc electroplating is conventionally carried out in alkaline baths which contain cyanide, which has a beneficial effect in achieving a bright, uniform zinc plate over a wide range of current densities. However, the increasing expense of using cyanide containing baths with the attendent waste disposal problems has lead to the development of cyanide-free plating baths. One technique for cyanide-free alkaline zinc electroplating involves use of a plating bath comprising sodium zincate electrolyte. Unfortunately, cyanide-free baths are commonly sensitive to build-up of both metallic and organic contaminants in the plating system. While the bath may initially perform well, it is subject to deteriorating performance as increasingly dark deposits may be encountered upon subsequent bright dipping passivation steps.
In accordance with the present invention, a novel compound has been discovered which is broadly useful as an additive in alkaline zinc electroplating baths. Thus, the novel compound of the present invention is useful as a brightener and anti-staining additive to cyanide-containing alkaline zinc electroplating baths and is particularly useful as a brightener and anti-staining additive to alkaline zinc plating baths which are cyanide-free such as sodium zincate baths. The plating baths of this invention are suitable for zinc plating over a wide current density range and are useful with all types of conversion coatings including chromate and non-chromate conversion coatings.
Further understanding of the present invention will be had from the following disclosure wherein all parts and percentages are by weight unless specifically indicated otherwise.